DPS Meter

GGG doesn't like to expose too much information, especially precise numbers, so I doubt that will ever happen. They seem to love the fact that stuff is a bit hidden / obscure.
But yeah, a combat log would be nice.

Probably because we'd discover even more bugs. I remember in the early days none of the damage on tooltips was accurate.

Not really.. I'm sure they'd love to have precise feedbacks with numbers about bugs.
They just don't like everything that might taint the game experience / screen with clutter, that's why they opposed health bars on monsters for so long, that's why they still oppose combat text on top of monsters even if they did build and test it internally if I remember well, and finally decided to ditch it.

https://www.pathofexile.com/forum/view-thread/686/1
good old times :D